Miller's contract was selected from Triple-A Sacramento on Thursday.
Miller joined the Giants on a minor-league deal in June and posted a 3.62 ERA and 1.25 WHIP in 32.1 innings over 27 appearances (one start) at Sacramento over the last few months. He posted a 9.24 ERA in 12.2 innings over 13 relief appearances between the Pirates and Cubs last year and should serve mainly as a low-leverage reliever for the Giants after Cole Waites was sent down Thursday.